1. Field of the Invention
The present invention relates to a system for encoding and decoding speech and/or audio signals.
2. Background
In the last two decades, the Code Excited Linear Prediction (CELP) technique has been the most popular and dominant speech coding technology. The CELP principle has been subject to intensive research in terms of speech quality and efficient implementation. There are hundreds, perhaps even thousands, of CELP research papers published in the literature. In fact, CELP has been the basis of most of the international speech coding standards established since 1988.
Recently, it has been demonstrated that two-stage noise feedback coding (TSNFC) based on vector quantization (VQ) can achieve competitive output speech quality and codec complexity when compared with CELP coding. BroadVoice® 16 (BV16), developed by Broadcom Corporation of Irvine Calif., is a VQ-based TSNFC codec that has been standardized by CableLabs® as a mandatory audio codec in the PacketCable™ 1.5 standard for cable telephony. BV16 is also an SCTE (Society of Cable Telecommunications Engineers) standard, an ANSI American National Standard, and is a recommended codec in the ITU-T Recommendation J.161 standard. Furthermore, both BV16 and BroadVoice®32 (BV32), another VQ-based TSNFC codec developed by Broadcom Corporation of Irvine Calif., are part of the PacketCable™ 2.0 standard. An example VQ-based TSNFC codec is described in commonly-owned U.S. Pat. No. 6,980,951 to Chen, issued Dec. 27, 2005 (the entirety of which is incorporated by reference herein).
CELP and TSNFC are considered to be very different approaches to speech coding. Accordingly, systems for coding speech and/or audio signals have been built around one technology or the other, but not both. However, there are potential advantages to be gained from using a CELP encoder to interoperate with a TSNFC decoder such as the BV16 or BV32 decoder or using a TSNFC encoder to interoperate with a CELP decoder. There currently appears to be no solution for achieving this.